(a) Field of the invention:
This invention relates to the formation particularly of the image forming optical system of an inverted-design optical microscope.
(b) Description of the Prior Art:
Generally, in an inverted-design optical microscope, optical accessory mechanisms for differential interference microscopy and fluorescence observation are arranged below an objective, as a result, an image forming optical system is formed further below it and therefore a photographing optical system for photographing can not help being set also in a considerably lower part of the microscope body. FIGS. 1 to 3 schematically show an example of the arrangement and formation of an observing optical system and photographing optical system in a conventional microscope of this kind. In the drawings, the reference numeral 1 denotes a microscope body, 2 denotes an illuminating optical axis, 3 denotes a condenser lens, 4 denotes a stage, 5 denotes a revolver, 6 denotes an objective, 7 denotes an eyepice tube, 8 denotes a prism having a semi-transparent mirror surface 8a and totally reflective mirror surface 8b which is alternatively inserted into the light path of the objective 6 from outside through a handle 8c, 9 denotes mirrors, 10 denotes an eyepiece, 11 denotes a prism having mirror surfaces 11a and 11b which is alternatively inserted into the light path of a light having passed through the semi-transparent mirror surface 8a of the prism 8 from outside through a handle 11c, 12 denotes a photographing lens arranged within the light path of a light to be reflected by the mirror surface 11a of the prism 11, 13 denotes a 35mm-film camera capable of being attached to and removed from the microscope body 1, 14 denotes a photographing lens arranged within the light path of a light to be reflected by the mirror surface 11b of the prism 11, 15 denotes a large-size camera capable of being attached and removed from the microscope body and 16 denotes a focusing glass arranged in an image forming position by the objective 6 and capable of being inserted into the light path of a light to be reflected by the semi-transparent mirror surface 8a from outside through a handle 16a. As shown in FIG. 3, when the handle 8c is switched to a position I and the handle 11c is switched to a position II, a light from an object to be inspected having passed through the objective 6 will be reflected by about 20% by the mirror surface 8a, will reach the eye of an observer through the eyepiece 10, will pass by about 80% through the mirror surface 8a, will be reflected by the mirror surface lla of the prism 11, will then pass through the photographing lens 12 and will reach the film surface of the camera 13. Therefore, in this state, if the handle 11c is switched to a position I, the light from the object to be inspected having passed through the mirror surface 8 a will be reflected by the mirror surface 11b of the prism 11, will pass through the photographing lens 14 and will reach the film surface of the large-size camera 15 attached to the camera body 1. Then, if the handle 8c is switched to a position II, the light from the object to be inspected having passed through the objective 6 will be all reflected by the mirror surface 8b and will reach the eye of the observer. In either of the above mentioned cases, if the handle 16a is switched to a position I, the focusing glass 16 will enter the observing light path. Therefore, in this state, a focusing can be made.
As described above, in the conventional inverteddesign optical microscope, as the photographing optical system for photographing is arranged below the observing optical system and the passing light is led selectively to two kinds of photographing optical systems, there are various defects together with the restriction that inherently the photographing optical system can not help being set in a considerably lower part of the microscope body 1. That is to say, due to the restriction of the camera size, in either of the small film-size camera 13 and the largesize camera 15, it is necessary that the photographing optical system, that is, the photographing light path should be on a fixed level above the surface of a desk on which the microscope body 1 is to be placed. For example, in the case of using a single-lens reflex camera equipped with a motor driving device as a camera to be attached outside, the center of the photographing light path must be on a level not less than 100 mm. above the desk surface. However, in order to meet this requirement, due to such restriction on the layout in the vertical direction as is described above, the stage 4 will result to be on a level not less than 330 mm. above the desk surface. Thus, the stage 4 will be so high that the operation of the inspected object on the stage surface will be difficult, the stage handle will have to be long and the operability will be impaired. Therefore, it is not desirable.
Also, as described above, in order to lead the photographing light path to the camera attached outside, the prism 11, that is, the second reflecting optical element is required. However, in leading the light from the inspected object to the second reflecting optical element, the optical path length will be considerably wasted and therefore the photographing lens 12 will result in considerably coming into the microscope body 1. Therefore, in the case of improving the operations made with the handles 8c, 11c and 16a so as to be made by a mere switching operation with a single handle, a considerably special complicated operatively connecting mechanism will be required. This means that not only it will be impossible to realize a compact switching device but also the device will have to be so large that it will be difficult to keep the stage level low, the entire device will be expensive and the optical performance will deteriorate. By the way, as described above, in this kind of microscope, as the optical accessory mechanism is inserted below the objective, a lens for extending the image position forward is provided in front of the light path dividing element, that is, the prism 8. However, due to the magnification, there is a limit to the extension. In order to exceed the limit while meeting the magnication condition, a comparatively complicated optical system called a retrofocus type system will have to be adopted. Therefore, it will be difficult to transmit an image well corrected by the objective without impairing the good image.
Further, in the case of the conventional formation, the focusing glass 16 is only made to be able to be singly inserted into and removed from the observing optical path and therefore, by only viewing the visual field, the observer can not know which photographing optical system is in use.